Photonic integrated circuits with controllable interferometers

Abstract

A method includes receiving a plurality of quantum systems, wherein each quantum system of the plurality of quantum system includes a plurality of quantum sub-systems in an entangled state, and wherein respective quantum systems of the plurality of quantum systems are independent quantum systems that are not entangled with one another. The method further includes performing a plurality of joint measurements on different quantum sub-systems from respective ones of the plurality of quantum systems, wherein the joint measurements generate joint measurement outcome data and determining, by a decoder, a plurality of syndrome graph values based on the joint measurement outcome data.

What is claimed is: 
     
         1 . A photonic circuit comprising:
 a photon source system to generate photons;   a plurality of photonic detector circuits, a photonic detector circuit of the plurality of photonic detector circuits including:
 a plurality of input waveguides to receive the photons; 
 a plurality of interferometers to interfere the photons; and 
 a plurality of photon detectors to generate measurement data by detecting the photons, 
 the plurality of interferometers comprising a first interferometer that is coupled to the plurality of input waveguides and a second interferometer that is coupled to the plurality of input waveguides, an interferometer of the plurality of interferometers comprising a phase shifter to apply a phase shift to light in the interferometer; 
   an optical memory comprising one or more photonic delay lines that temporarily store one or more of the photons before the photons are input into the photonic detector circuits;   a plurality of electrical control lines to set phase shifts to be applied by the interferometers; and   a memory to store the measurement data generated by the plurality of photon detectors.   
     
     
         2 . The photonic circuit of  claim 1 , wherein the photon source system generates the photons using a probabilistic photon scheme. 
     
     
         3 . The photonic circuit of  claim 2 , wherein the probabilistic photon scheme comprises one of: a four wave mixing scheme or a spontaneous parametric down conversion scheme. 
     
     
         4 . The photonic circuit of  claim 1 , wherein another optical detector circuit of the plurality of photonic detector circuits generates additional measurement data using an additional plurality of photon detectors to detect additional photons. 
     
     
         5 . The photonic circuit of  claim 4 , wherein the other optical detector circuit comprises additional phase shifters having phase shifts that are controlled by additional electrical control lines, and wherein the memory stores the additional measurement data. 
     
     
         6 . The photonic circuit of  claim 1 , wherein the electrical control lines set at least one or more phase shifters such that the measurement data comprises XX and ZZ measurement data. 
     
     
         7 . The photonic circuit of  claim 1 , wherein the one or more photonic delay lines comprise one or more optical fibers. 
     
     
         8 . The photonic circuit of  claim 1 , wherein the photons comprise a first photon and a second photon, the first photon being generated at a first time and the second photon is generated at an earlier time that is before the first time. 
     
     
         9 . The photonic circuit of  claim 8 , wherein the second photon is stored in the optical memory such that detections of the first photon and the second photon by the plurality of photon detectors coincide to generate the measurement data. 
     
     
         10 . A method comprising:
 generating photons using a photon source system of a photonic circuit;   temporarily storing one or more of the photons in an optical memory comprising one or more photonic delay lines;   receiving the photons, including the temporarily stored photons from the optical memory, on a plurality of input waveguides of a photonic detector circuit of the photonic circuit;   interfering the photons on a plurality of interferometers of the photonic detector circuit, the plurality of interferometers comprising a first interferometer that is coupled to the plurality of input waveguides and a second interferometer that is coupled to the plurality of input waveguides, an interferometer of the plurality of interferometers comprising a phase shifter to phase shift light in the interferometer, phase shifts of the phase shifter being controlled by one or more electrical control lines;   generating measurement data by detecting the photons on one or more detectors of a set of detectors in the photonic detector circuit; and   storing the measurement data in memory of the photonic circuit.   
     
     
         11 . The method of  claim 10 , wherein generating the photons comprises generating the photons using a probabilistic photon scheme. 
     
     
         12 . The method of  claim 11 , wherein the probabilistic photon scheme comprises one of: a four wave mixing scheme or a spontaneous parametric down conversion scheme. 
     
     
         13 . The method of  claim 10  further comprising generating additional measurement data using an additional plurality of photon detectors to detect additional photons. 
     
     
         14 . The method of  claim 13 , wherein the other optical detector circuit comprises additional phase shifters having phase shifts that are controlled by additional electrical control lines, and wherein the memory stores the additional measurement data. 
     
     
         15 . The method of  claim 10 , wherein the electrical control lines set at least one or more phase shifters such that the measurement data comprises XX and ZZ measurement data. 
     
     
         16 . The method of  claim 10 , wherein the one or more photonic delay lines comprise one or more optical fibers. 
     
     
         17 . The photonic circuit of  claim 1 , wherein the electrical control lines set at least one or more phase shifters such that the measurement data comprises XZ and ZX measurement data. 
     
     
         18 . The method of  claim 10 , wherein the electrical control lines set at least one or more phase shifters such that the measurement data comprises XZ and ZX measurement data. 
     
     
         19 . The photonic circuit of  claim 1 , wherein a logical qubit comprises a plurality of vertices of a topological code comprising multiple physical qubits, wherein the photons correspond to the physical qubits, and wherein the measurement data is usable to construct syndrome data associated with the plurality of vertices. 
     
     
         20 . The method of  claim 10 , wherein a logical qubit comprises a plurality of vertices of a topological code comprising multiple physical qubits, wherein the photons correspond to the physical qubits, and wherein the measurement data is used to construct syndrome data associated with the plurality of vertices. 
     
     
         21 . The photonic circuit of  claim 1 , wherein the photon source system generates the photons using one or more quantum dots. 
     
     
         22 . The method of  claim 10 , wherein generating the photons comprises generating the photons using one or more quantum dots.